The present invention relates to the control of fuel vapor from a fuel tank to an engine air inlet and to a storage canister.
A known system for preventing the emission of fuel vapor to the atmosphere is shown in FIG. 2 where vapor from a fuel tank 1 flows through a conduit 2 to a conduit junction 3 which is connected to an electrically operated purge control valve 4 and also to a storage canister 5 which is connected through an electrically operated valve 6 to atmospheric. The valve 4 is electrically controlled by an engine computer 7 and has its outlet connected to the air intake manifold of the vehicle engine denoted by reference numeral 8.
In operation, upon engine start up and opening of the purge control valve 4, the known system of FIG. 2 draws vapor from both the fuel tank and the storage canister through junction 3 which effects a purging of the storage canister but can also result in a high vacuum being drawn in the fuel tank.
Furthermore the known system of FIG. 2 has the disadvantage that during periods of high air inlet depression or high vacuum the restricted flow from the canister may cause a high vacuum to be pulled in the fuel tank causing increased vaporization of fuel in the tank.
Thus, it has been desired to provide a way or means of controlling flow of fuel vapor from a tank which accommodates both the prevention of fuel emission to the atmosphere and provides for flow to the engine air intake manifold and prevents damage to the system components.
The present invention provides a pressure differential responsive control valve disposed in the fuel vapor vent line of a vapor emission control system and prevents the engine air inlet induction from drawing a vacuum in the fuel tank yet permits a relatively high flow of fuel vapor to a storage canister when the purge valve is shut off.
The valve of the present invention provides a spring biased valve in the valving chamber inlet port from the tank vapor line; and, the chamber is in open communication with a first outlet to the engine air intake manifold through the purge valve and a second outlet to the storage canister. The spring bias on the valve is varied by a pressure responsive diaphragm which responds to the pressure differential between the pressure in the valving chamber and the atmospheric pressure. The valve of the present invention is spring biased to close the vent line from the tank in response to high engine induction vacuum thereby reducing the vapor flow from the fuel tank, yet maintains open communication between the canister and the engine inlet vapor purge valve. A bleed passage is provided to prevent vapor pressure build up in the fuel tank.